Poison ivy is an allergenic plant in the genus Toxicodendron native to Asia and North America. It is well known for causing urushiol-induced contact dermatitis, an itchy, irritating, and sometimes painful rash, in most people who touch it. The rash is caused by urushiol, a clear liquid compound in the plant's sap. The plant is variable in its appearance and habit, and despite its common name, it is not a true ivy (Hedera), but rather a member of the cashew and pistachio family (Anacardiaceae). T. radicans is commonly eaten by many animals, and the seeds are consumed by birds, but poison ivy is most often thought of as an unwelcome weed. Poison ivy was formerly treated as a single species, Toxicodendron radicans, but is now generally treated as a complex of three separate species: Toxicodendron radicans (eastern poison ivy), Toxicodendron rydbergii (western poison ivy) and Toxicodendron orientale (Asian poison ivy).
Poison ivy is characterized by leaves each containing three leaflets, hence the common expression "leaves of three, let it be". Poison ivy is a low shrub or tall vine with small flowers, developing whitish fruits in fall.
- Toxicodendron orientale (Asian poison ivy), found in East Asia.
- Toxicodendron radicans (eastern poison ivy), found throughout eastern Canada and the United States, Mexico and Central America, Bermuda and the Bahamas.
- Toxicodendron rydbergii (western poison ivy), found throughout Canada and much of the United States excepting the southeast.
Urushiol-induced contact dermatitis is the allergic reaction caused by poison ivy. In extreme cases, a reaction can progress to anaphylaxis. Around 15 to 25 percent of people have no allergic reaction to urushiol, but most people have a greater reaction with repeated or more concentrated exposure. Typically, the rash from the urushiol oil lasts about five to twelve days, but in extreme cases it can last a month or more.
Over 350,000 people are affected by urushiol annually in the United States.
The pentadecyl catechols of the oleoresin within the sap of poison ivy and related plants causes the allergic reaction; the plants produce a mixture of pentadecylcatechols, which collectively is called urushiol. After injury, the sap leaks to the surface of the plant where the urushiol becomes a blackish lacquer after contact with oxygen.
Urushiol binds to the skin on contact, where it causes severe itching that develops into reddish inflammation or uncoloured bumps, and then blistering. These lesions may be treated with Calamine lotion, Burow's solution compresses, dedicated commercial poison ivy itch creams, or baths to relieve discomfort, though recent studies have shown some traditional medicines to be ineffective. Over-the-counter products to ease itching—or simply oatmeal baths and baking soda—are now recommended by dermatologists for the treatment of poison ivy.
A plant-based remedy cited to counter urushiol-induced contact dermatitis is jewelweed, though jewelweed extracts had no positive effect in clinical studies. Others argue that prevention of lesions is easy if one practices effective washing, using plain soap, scrubbing with a washcloth, and rinsing three times within 2–8 hours of exposure.
The oozing fluids released by scratching blisters do not spread the poison. The fluid in the blisters is produced by the body and it is not urushiol itself. The appearance of a spreading rash indicates that some areas received more of the poison and reacted sooner than other areas or that contamination is still occurring from contact with objects to which the original poison was spread. Those affected can unknowingly spread the urushiol inside the house, on phones, door knobs, couches, counters, desks, and so on, thus in fact repeatedly coming into contact with poison ivy and extending the length of time of the rash. If this has happened, wipe down the surfaces with bleach or a commercial urushiol removal agent. The blisters and oozing result from blood vessels that develop gaps and leak fluid through the skin; if the skin is cooled, the vessels constrict and leak less. If plant material with urushiol is burned and the smoke then inhaled, this rash will appear on the lining of the lungs, causing extreme pain and possibly fatal respiratory difficulty. If poison ivy is eaten, the mucus lining of the mouth and digestive tract can be damaged. An urushiol rash usually develops within a week of exposure and can last 1–4 weeks, depending on severity and treatment. In rare cases, urushiol reactions may require hospitalization.
Urushiol oil can remain active for several years, so handling dead leaves or vines can cause a reaction. In addition, oil transferred from the plant to other objects (such as pet fur) can cause the rash if it comes into contact with the skin. Clothing, tools, and other objects that have been exposed to oil should be washed to prevent further reactions.
People who are sensitive to urushiol can also experience a similar rash from mangoes. Mangoes are in the same family (Anacardiaceae) as poison ivy; the sap of the mango tree and skin of mangoes has a chemical compound similar to urushiol. A related allergenic compound is present in the raw shells of cashews. Similar reactions have been reported occasionally from contact with the related Fragrant Sumac (Rhus aromatica) and Japanese lacquer tree. These other plants are also in the family Anacardiaceae.
Immediate washing with soap and cold water or rubbing alcohol may help prevent a reaction. During a reaction, Calamine lotion or diphenhydramine may help mitigate symptoms. Corticosteroids, either applied to the skin or taken by mouth, may be appropriate in extreme cases. An astringent containing aluminum acetate (such as Burow's solution) may also provide relief and soothe the uncomfortable symptoms of the rash.
Similar allergenic plants
- Gluta spp (rengas tree)
- Lithraea molleoides (aruera – South America)
- Smodingium argutum (African poison ivy)
- Toxicodendron pubescens (poison oak – eastern)
- Toxicodendron diversilobum (poison oak – western)
- Toxicodendron vernix (poison sumac)
- Toxicodendron vernicifluum (Japanese lacquer tree)
- Innes, Robin J. (2012). "Toxicodendron radicans, T. rydbergii". Fire Effects Information System (FEIS). US Department of Agriculture (USDA), Forest Service (USFS), Rocky Mountain Research Station, Fire Sciences Laboratory – via https://www.feis-crs.org/feis/.
- "LEAVES OF THREE, LET IT BE: HOW TO AVOID POISON IVY AND ITS ITCHY RASH". Reconnect with Nature. Forest Preserve District of Will County. Retrieved 19 October 2020.
- "Toxicodendron rydbergii". Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 19 October 2020.
- "Toxicodendron orientale". Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 19 October 2020.
- "Toxicodendron radicans". Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 19 October 2020.
- "How Poison Ivy Works". HowStuffWorks.
- Rohde, Michael. "Contact-Poisonous Plants of the World". mic-ro.com.
- "Poison Ivy, Poison Oak and Poison Sumac FAQs".
- Chaker, Anne Marie; Athavaley, Anjali (June 22, 2010). "Least-Welcome Sign of Summer". The Wall Street Journal. p. D1.
- Barceloux, Donald G. (2008). Medical Toxicology of Natural Substances: Foods, Fungi, Medicinal Herbs, Plants, and Venomous Animals. John Wiley and Sons. pp. 681–. ISBN 978-0-471-72761-3.
- Rietschel, Robert L.; Fowler, Joseph F.; Fisher, Alexander A. (2008). Fisher's contact dermatitis. PMPH-USA. pp. 408–. ISBN 978-1-55009-378-0.
- Wilson, W. H. & Lowdermilk, P. (2006). Maternal Child Nursing Care (3rd edition). St. Louis: Mosby Elsevier.
- "American Topics. An Outdated Notion, That Calamine Lotion". Archived from the original on 2007-06-19. Retrieved 2007-07-19.
- Appel, L.M. Ohmart; Sterner, R.F. (1956). "Zinc oxide: A new, pink, refractive microform crystal". AMA Arch Dermatol. 73 (4): 316–324. doi:10.1001/archderm.1956.01550040012003. PMID 13301048.
- "American Academy of Dermatology – Poison Ivy, Oak & Sumac". Archived from the original on 2009-06-05.
- Long, D.; Ballentine, N. H.; Marks, J. G. (1997). "Treatment of poison ivy/oak allergic contact dermatitis with an extract of jewelweed". Am. J. Contact. Dermat. 8 (3): 150–3. doi:10.1097/01206501-199709000-00005. PMID 9249283.
- Gibson, MR; Maher, FT (1950). "Activity of jewelweed and its enzymes in the treatment of Rhus dermatitis". Journal of the American Pharmaceutical Association. 39 (5): 294–6. doi:10.1002/jps.3030390516. PMID 15421925.
- Guin, J. D.; Reynolds, R. (1980). "Jewelweed treatment of poison ivy dermatitis". Contact Dermatitis. 6 (4): 287–8. doi:10.1111/j.1600-0536.1980.tb04935.x. PMID 6447037. S2CID 46551170.
- Zink, B. J.; Otten, E. J.; Rosenthal, M.; Singal, B. (1991). "The effect of jewel weed in preventing poison ivy dermatitis". Journal of Wilderness Medicine. 2 (3): 178–182. doi:10.1580/0953-9859-2.3.178.
- Extreme Deer Habitat (2014-06-22). "How to never have a serious poison ivy rash again". Retrieved 2016-07-26.
- "Facts about Poison Ivy: How long does the rash last?, What can you do once the itching starts?, How do you get poison ivy?". poison-ivy.org.
- Editors of Prevention (2010). The Doctors Book of Home Remedies: Quick Fixes, Clever Techniques, and Uncommon Cures to Get You Feeling Better Fast. Rodale. pp. 488–. ISBN 978-1-60529-866-5.CS1 maint: extra text: authors list (link)
- Lewis, Robert Alan (1998). Lewis' dictionary of toxicology. CRC Press. pp. 901–. ISBN 978-1-56670-223-2.
- "Poison Ivy, Oak & Sumac". aad.org. Archived from the original on 2007-07-08.
- "Poision ivy - oak - sumac". MedlinePlus Medical Encyclopedia. A.D.A.M., Inc. Retrieved 16 June 2019.
- Tucker, Mark O.; Swan, Chad R. (1998). "The Mango–Poison Ivy Connection". New England Journal of Medicine. 339 (4): 235. doi:10.1056/NEJM199807233390405. PMID 9673302.
- Rosen, T.; Fordice, D. B. (April 1994). "Cashew Nut Dermatitis". Southern Medical Journal. 87 (4): 543–546. doi:10.1097/00007611-199404000-00026. PMID 8153790.
- "Misconceptions About Treating Poison Ivy and Oak Rash". teclabsinc.com. Archived from the original on 2014-08-26.
- Gladman, Aaron C. (June 2006). "Toxicodendron Dermatitis: Poison Ivy, Oak, and Sumac". Wilderness & Environmental Medicine. 17 (2): 120–128. doi:10.1580/PR31-05.1. PMID 16805148.
- "Botanical Dermatology – ALLERGIC CONTACT DERMATITIS – ANACARDIACEAE AND RELATED FAMILIES". The Internet Dermatology Society, Inc. Retrieved 22 Sep 2014.